How tight junctions might prevent small charged solutes from entering the brain (across the blood-brain barrier) was made clear by our previous model of tight junction structure based on a lipidic backbone. This model has been discussed and elaborated in several publications in recent years. A new study of the gap junctions in murine cells by freeze-fracture and freeze-substitution has been completed showing that these gap junctions show considerable structural diversity, falling into there types. One type is so aberrant from typical gap junction structure as to question its categorization as an electrotonic junction. This work has now been published and this project in now in abeyance.